Preparation of alkylene cyanohydrins



Dec, ll, 1945.

H. S. DAVIS ET AL PREPARATION OF ALKYLENE CYANOHYDRINS Filed Feb. 16,1939 INVENTORS, /VZ 5. @4V/v5', BY ffy/V C. ,Pip/170,

; ddevhw/ ATTORNEY.

Patented Dec. 11, 1945 PREPARATION OF ALKYLENE CYANOHYDRINS lHarold S.Davis and Bryan C. Redmon, Riverside,

Conn., asslgnors to Amer'can Cyanamid Company, New York, N. Y., acorporation of Maine Application February 16, 1939, Serial No. 256,676

13 Claims.

The present invention relates to a method of making alkylenecyanohydrins from the correspending alkylene oxide and hydrocyanic acid,in

the liquid phase. l

The reaction using ethylene oxide as a typical starting material may bewritten asfollows:

Inasmueh as the boiling point, at atmospheric pressure, of ethyleneoxide is 10.7 C., that of HCN is 26 C., and that of vethylenecyanohydrin is 220 C., and since the operating temperatures are muchabove the boiling point of the reactants, it is, therefore, necessary toallow the reaction to proceed in closed systems under pressure due tothe high vapor pressures of the initial reactants at the operatingtemperatures.

The prior art indicates that the reaction is a slow one. Erlenmeyer(Liebigs Annalen 191,261, (1878)) reports a yield at 25 C. in closedtubes after eight days, but a good yield at 50 to 60 C. after four days.No further definition as to yields is mentioned by this experimenter.

The principal object of the present invention, therefore, is to discoverways and means for reacting the alkylene oxides and hydrocyanic acid sothat commercial yields are obtainable in simple `apparatus in muchshorter periods of time.

Using ethylene oxide as an example, simply because the prior artliterature deals with this reactant in the preparation of ethylene`cyanohydrin and because of its cheapness and availability, it has nowbeen determined that at higher temperatures than those heretoforedescribed, a spontaneous, rapid and highly exothermic reaction occurswith HCN to form ethylene cyanohydrin in good yields if equi-molecularmixtures of the reactants `are heated under pressure to withinanactivation temperature range in which the reaction starts spontaneously.Cnce started, the reaction has been observed to proceed under its ownpower at a velocity depending principally upon the extent of theydilution of the reactants in certain solvents. When the reaction isspontaneously under way, it is no longer necessary to supply heat to thesystem unless the reaction has been `caused t-o proceed very slowly.

The heat oi' reaction has been calculated from the known heats offormation .oi HCN and ethylene oxide and from an estimated value forethylene cyanohydrin. The heat of reaction so calculated was found to bebetween +40,000 and +50,000 calories per mol of liquid ethylenecyanohydrin formed from liquid reactants. 'This corresponds to from 550to 700 calories per gram.

If no diluent is present and no heat lost to the container orsurroundings, the heat of reaction will raise the reaction product to apoint substantially in the neighborhood of 1000" C. above the activationtemperature with a corresponding pressure increase. It has been foundthat such high temperatures very seriously impair the yields due todestruction of the product and possibly of the initial reactants throughpyrolysis and polymerization. It is, therefore, a matter of the utmostimportance to avoid excessive temperature rises during the reaction.This may be accomplished by controlling the reaction velocity so thatsuicient time is permitted for heat dissipatien, carrying out thereaction in an apparatus designed to conduct the heat away quickly andefficiently or dissolving the reactants in a suitable solvent whichdecreases the reaction velocity and assists ln heat dispersion, orcombinations of the above.

It is, of course, equally disadvantageous to allow 4 the temperature ofthe reaction to fall much below the activation range since this eitherstops the reaction completely or slows up its velocity undesirably.Therefore, a temperature somewhat above the minimum activationtemperature should be maintained as closely as possible. While the exactvalue of these tempel atures will depend upon the conditions of thereaction and the design of the apparatus, in general it may be said thatthe activation temperature lies between thelimits of 90 C. and 150 C.and, consequently,

- in temperature and pressure. It may be generally said that solvents ofwhich a mixture of aiphenyl oxideand diphenyl with a boiling pOnt ofsubstantially 250 C. to 260 C., and ethylene glycol are typical havenot.been found to be of value. Solvents of the polar type, however, suchas water, ethylene cyanohydrin and the liquid reaction product of a.previous run, have a very marked effect in rendering the velocity of thereaction controllable. Water, however, has the disadvan- 'tage ofpromoting the corrosion of steel by HCN where the reaction is carriedout in apparatus including that material. However, the use oi the moreresistant alloy steels under these circumstances will be desirable inview of the cheapness of this diluent.

When a quantity of the liquid product from a previous run was used as adiluent. the amazing discovery was made that i-t was possible to startlowing data.

l the reaction at rather low activation temperatures, and to control thereaction velocity over Wide ranges by merely varying the concentrationof the reactants. The use of ordinary or commercial alkylene yanohydrinsin this manner 5 98% product and contained some HCN polymer as evidencedby its yellow color. It would seem, therefore, that even the smallamount of polymer present in the commercial HCN used renders thereaction more controllable. Compare runs 3 and 4 for this eiect.

In run 2, it is concluded that the absence of a diluent caused loss ofcontrol after the reaction was initiated andthe apparatus exploded.

` TABLE 1I Reactions in steel bomb [Water as diluent] Conc. ofActivation Pressure at Highest Tem in- Hl he t reactants Catalyst temp.act. temp. temp. cregse pregsue Yield per um 0. Loa/aq. in. o. c.Lbs/sq. in. Per um 50 None 121i 100 168 45 200 i l Large amount of HCNpolymer.

TAeLa III Reactions in glass bombs [Commercial ethylene cyanohydrin as adiluent] Activa- High- Temp Conc. of Pressure at Highest Time ofreactants 3111). act. temp. tfltp 15m pressure reaction Yield Per centC. LbsJsq. in. C. C. LbaJaq. in. Minuta Per cent 130 32 132 2 l 32 30-3525 17. 2 128 75 136 8 75 10-15 V73 33.3 115 68 130 15 83 5-10 55 50.0108 150 300 (l) l Explosion.

TABLI: IV

Reactions in steel bomb [Commercial ethylene cyanohydrin as a diluent]Activa- High- 'rem Conc. of Pressure at p Highest Time of reactants agg;act. temp. tu 81.21886 pressure reaction Yleld Per cem C'. Lba/sg. in.C'. C. Lbaa .11. Mui/,tss Pe t m 112 58 122 10 l a63 Ca. 26 Tgfin 118 70134 16 85 Ca. 8 80 34 118 100 141 Z3 100 C8. 5 38-51 110 10() 164 54 800C8. 3 0

tion products or even unreacted starting materials which act ascatalysts, although obviously we do not wish to be limited to such a.theory.

In this connection, reference is had to the fol- In all cases, theconcentration of the reactants is based upon the weight percentage f ofthe equi-molecular mixture of the reactants in 'Ihese data showgenerally that in the apparatus used, the reaction rate is the fastestand centrations of reactants, and, correspondingly, as the concentrationis decreased, the reaction velocity and hence the temperature andpressure the total weight of solution. increases are diminished. It isalso at once ap- TABLE I Reactions in' glass bombs [Water as diluent]Activa- Conc, of Pressure et Highest Temp. Highest Time of reactantsCatalyst tgx act. temp.V temp. increase pressure reaction Yield Lba/sq.in. f 01.10 C. LbL/aq. in. Minuta Percent 1 No reaction after 3 hoursand 10 minutes. I Explosion. i Used pure distilled HCN and ethyleneoxide.

In Table I above, it is to be noted that With the parent that the mostrapid reactions, giving rise to higher temperatures, give lower yieldsthan the slower reactions. This phenomenon may be ascribed to thedestruction of the product at Y higher temperaturesJ which is coniirmedby the large amounts of polymer and undistillable substances left ondistilling the product. In general, the activation temperatures decreasewithV increasing concentrations in glass, but in steel this eilect isnot generally noticeable. It seems probable that the presence of ironlowers the activation temperatures in al1 cases since one rea action inglass showed a decrease of 18 C. (128 to" 110 C.) in the activationtemperature when the reaction was carried out in the presence of ironwires. A decrease in activation temperature is also always accompaniedby a decrease in the highest temperature and pressure attained in thereaction, so that iron may be said .to have a.

Vbeneficial eil'ect.

- tards it. This leads to the 4conclusion that the presence of CN- ionis believed to be necessary if the reaction is to proceed. The existenceof this ion is indicated in the presence of bases and water. The absenceof CN ion in the presence of acids, due to the repression or ionizationof HCN may explain the negative eilect of acids. and the removal oi.'CN- ions due to formation oi complex ions of copper and CN- may explainthe negative eiect of metallic copper.

The foregoing data. also show that the best yields yet attained withcyanohydrin as diluent were 80% and these were obtained in 20-25%solutions. These concentrations were optimum where no particular attemptwas made to dissipate the heat of reaction from the apparatus. Aconcentration of 25%, therefore, may be exceeded where means jareprovided to abstract rapidly the reaction heat.

Runs were carried out to investigate the eilect of recycling, using thereaction product from each run as a solvent for the next run without anyintermediate treatment. In `two series of such runs, 20% solutions werereacted in a steel bomb. Three and two cycles were lrun so that thepercentage composition of the mixtures was) substantially the same. Thefollowing data were It is apparent from an inspection of Table V thatsome substance present in the product exerts a marked effect in loweringthe activation temperature. Hence, the maximum temperatures andpressures attained are decreased in reactions when the product i'rom onerun is used withoutturther treatment as the solvent for the next run.Such conditions would be encountered in recycling. It should also bepointed out that in each successive run or cycle the reaction velocitybecomes more rapid (about 100% faster each cycle) althoush thetemperatures and pres- 'sures are lower.

The following pertinent facts concerning the reaction may be outlined:

1. The reaction is spontaneous and exothermic when the reactants areheated to a suitable activation temperature, that is, above 00 0.

2. Once started. the reaction will proceed rapidly, depending upondilution and it without heat dissipation, the temperature may rise aboveC. which is undesirable.

3. Where the concentration oi' reactants is between 15% and 5,0%. in asuitable diluent. the reaction proceeds smoothly with sood yields.

4. The entire desirable temperature range over which the reaction takesplace is controllable by choice of reactant dilution and/or heatdissipation.

5. Substances s exerting an alkaline eil'ect and/or pe itting theformation of CII'- ions lower the activation temperature of the rction.Some such substances are:

Water Alkylene cyanohydrin l 'I'he liquid product of a previous runAlkali-forming metal oxides Alkali-forming metal hydroxides PyridineAmines Ammonia HCN polymer Tear.: VI

Reaction in glass bomb [Propylene oxide, HON with water as diluent]Pressure of activation temp.

Activation temp.

Maxlmum pressure Time of reaction Conc. `of

Temp. reactants in' Yield @N888 C'. Ca. 167

Per cent 74. 3

Per cent Pounds Minutes 70 480 m The product of this reaction wasidentied as propylene cyanohydrin most likely having the formula-CHHI--cfJ-n cN on and the following physical constants:

Refractive index 1.4280 at 20.5 C. Boiling point at 768 mm. 208 C.Boiling point at 760 mm. 207 C. Boiling point at 15 mm. 104 C. Density0.9942 at 20 C.

It is to be noted, however, that as the higher members of the series ofoxides have longer carbon chains, the activation temperature of their2,890,519 l p 1 s. The method of claims whue stamane the reaction withHCN will increase correspondingly.

In preparing such a ,cyanohydrlm the same general conditions as foundfor ethylene cyano-` hydrin have been observed.

All these factors point to the use of a continuous process in steelpressure apparatus for the manufactureA of ethylenev and other alkylene`some other diluent and/or catalyst. Of course,

the catalyst and/ or diluent may be fed separately. 'I'he vessel is thenclosed and heated to the activation temperature. At this point, acooling mel dium is supplied to maintain the temperature and pressurewithin optimum limits? so as to obtain desirable yields. A portion ofthe reaction product together with unreacted reactants, if any,l is thenrecycled with or without additions of a diluent and/or catalyst asindicated. The major portion of the contents of the reaction vessel arethen passed to a separation still where the unreacted reactants, if any,are removed to give a reaction product of requisite quality.

While the invention has been described with particular reference tospecific embodiments, it is to be understood that it is not to belimited thereto, but is to be construed broadly, and limited solely bythe scope of the appended claims.l

We claim: y

1. A method of making alkylene cyanohydrin which' includes the steps ofreacting an alkylene oxide and HCN in liquid phase at a temperaturegreater than 90 C.

2. The method of claim 1 while 'abstracting the heat of reaction so asto maintain the reaction vessel at a temperature not greater than 150 C.

3.. A method of making-alkylene cyanohydrin which' includes the steps ofreacting an' alkylene oxide and HCN in liquidphase -at a. ,temperaturelgreater-than 90?' CQ-in whichthereaction is carried out in the presenceof alkylene cyanohydrin Ithe latter being present in the proportion offrom 4. A method ofmaking lalkylene cyanohydrin which' includes thesteps of reacting an alkylene oxide and HCN in liquid phase at atemperature greater than 90 C. in which the reaction is carried out inthe presence of a quantity of the liquid reaction product of a previousrun the latter being present inthe proportion of from 34 -to 82%.

5. A method of making ethylene cyanohydrin which includes the steps ofreacting an ethylene oxide and HCN in liquid phase at a temperaturegreater than 90 C.

heat of reaction so as tol maintain the reaction vessel at a temperaturenot greater than 150 C.

7. The method of claim 5 in which the reaction is carried out in thepresence of a liquid chosen from the group consisting vof water,ethylene Vcyanohydrin and the liquid product of a previous run theIlatter being present in the proportion of from 34 to 82%.

greater than 90 C. in which the reaction is carried out in the presenceof a quantity of the liquid reaction product of a previous run thelatter being present in the proportion of from34 to 82%..

10. A method `of making ani alkylene cyanohydrin which includes thesteps of heating an alkylene oxide and HCN in liquid phase to anactivation temperature in whichthe reaction starts spontaneously inwhich the-concentration of reactants is from 15% to 50% in a diluent,th'e major portion of which is alkylene cyanohydrin.

11. A method of making an alkyiene cyanohydrinwhich includes the' stepsof heating an alkylene oxide and HCN in liquid phase to an activationtemperature in which the reaction` starts spontaneously in which' theconcentration of reactants is from 15%Mto 50% 'in a diluent, the majorportion of whichiisfalkylene 'cyanohydrim While abstracting theliea't'iof reaction so as mainpamthetemperature-'below15050. i:

`12. A' continuous.processfoffmaking alkylene cyanhydrinr'whi'chincludes' the steps of'feeding alkylen'e oxide andihydrocyanicacid to areaction zone heated'to from90 C.-to 150 C., together with the productot a previous run, drawin'goil the resultant cyanh'y'drin product, andrecyclingrv a portion thereof together" with fresh1quantities ofalkylene oxide and 'hydrocyanic acid to reaction zone.

13. A continuous process of making alkylerie"l cyanhydrin, whichincludes the steps of feeding alkylene oxide and hydrocyanic acid to areaction zone heated to from C. to 1 50 C., together with the product ofa previous run. drawing on the resultant cyanhydrin product, andrecycling a por-

